various agricultural agencies, Emphasis in this discussion 
is placed on the relation of SNC to the production of wild- 
life, primarily upland nesting waterfowl and game birds, 
and to land being managed within the National Wildlife 
Refuge System. 
Residual Cover in Spring 
Kirsch et al. (1978) reported on a direct relation be- 
tween increasing duck nest densities and success of 
clutches and increasing visual obstruction of residual vege- 
tation in spring. In view of their data, the potential for 
maximum production of most species of upland nesting 
ducks should be anticipated in the taller and denser 
residual vegetation and likewise, higher measurements of 
plant height and visual obstruction should be predictive of 
stand performance and of the potentiality of higher wild- 
life outputs. 
Results of the present study indicate that the maximum 
vegetation growth for individual SNC stands can be iden- 
tified by visual obstruction and height measurements of 
residual vegetation in spring. A stand apparently reaches 
maximum growth in only 1 of the first 10 years. Stands 
usually reach their maximum growth during either the 
third, fourth, or fifth growing season but the specific year 
in which a stand will reach its maximum growth is too 
variable to predict. Stands also tend to degenerate in 
height and visual obstruction value after the year of maxi- 
mum growth. The degeneration does not always occur in 
a predictable pattern and, as with the year of maximum 
growth, several environmental factors contribute to this 
variability. Precipitation apparently affected stand 
growth and performance the most, especially the amount 
received in the year before spring measurements and the 
amount of snow and ice received in the previous winter, 
The effect of individual SNC species on visual obstruc- 
tion and height measurements varied in spring. Tall 
wheatgrass provided greater visual obstruction than inter- 
mediate wheatgrass, slender wheatgrass, or quackgrass, 
principally because of greater plant height, better reten- 
tion of standing dead seed stalks for at least 3 years, and 
the clumpy bunchgrass form. Sweet clovers, on the other 
hand, provided the tallest cover, just over 3 m in a stand, 
but visual obstruction was not as great as for grasses be- 
cause of lower plant densities. Red clover and alfalfa pro- 
vided poorer visual obstruction than grasses in spring be- 
cause of their greater tendency to lodge. 
Unlike a standing crop of live vegetation in summer, 
residual SNC in spring has been subjected to overwinter 
compaction and fracturing, harvesting by animals, and 
decomposition. Although residual SNC measurements in 
spring do not represent the truest aspect of stand perform- 
ance from a previous growing season, during an average 
winter they should represent a relative reflection of the 
structural qualities. In 2 of 3 years, representative per- 
formance of stands was mostly negated by ice, heavy 
snowpack, or a combination of snowpack and harvest by 

17 
rodents. Such events, if frequent, would therefore negate 
the possibility of setting minimum visual obstruction or 
plant height goals for vegetation or wildlife management 
purposes. For example, if a minimum threshold of 1.5 dm 
for total visual obstruction had been set as a decision point 
for vegetation management purposes in this study, treat- 
ments would have been applied to 23% of the sampled 
SNC stands in 1977, 93% in 1978, and 77% in 1979. 
Furthermore, 22% of the same stands that would have re- 
ceived treatment (<1.5 dm) in 1978 would not have 
needed treatment (> 1.5 dm) in 1979, a case in point of a 
potentially unnecessary and excessive treatment effort in 
1978. In some instances, a stand that is poor initially may 
never provide visual obstruction above a set threshold 
value for management purposes. 
There are no known published minimum values relating 
visual obstruction of residual vegetation to wildlife out- 
puts. However, preliminary results from related studies at 
Northern Prairie Wildlife Research Center indicate that 
minimum values vary in range by species or groups of 
species; average minimum values for mallards (Anas 
platyrhynchos) have been high compared with low aver- 
age values for upland sandpipers (Bartramia longicauda). 
Vegetative Cover in Summer 
Changes in structural features of SNC, including 
canopy cover, species composition, life-form, and number 
of species were greatest during the first three growing sea- 
sons and fairly constant during the next six growing sea- 
sons. When stands were properly established (Duebbert 
et al. 1981), the planted species dominated most stands for 
at least 10 years. Successful establishment of a stand was 
usually apparent in the second growing season. During the 
second growing season, SNC should be a fairly continuous 
but open crop with sweet clovers as the dominants, and in- 
termediate wheatgrass, tall wheatgrass, and alfalfa as the 
subdominants. The stand should also contain an assort- 
ment of annual forbs. During the third growing season, 
SNC should be dominated by a dense crop of intermediate 
wheatgrass, tall wheatgrass, and alfalfa and the stand 
should be intermixed with dead sweet clover stalks. 
Grasses should make up about 60-80% of the cover in the 
third growing season. 
Occasionally SNC stands showed no evidence of success- 
ful establishment in the second growing season because of 
the effects of drought, weed dominance, or improper seed- 
ing. During the third growing season, these stands would 
either become established, usually with a sparse mix of 
SNC, or they would become dominated by undesirable 
species of grasses and forbs. In either instance, a manage- 
ment decision for either retaining or replacing the stand is 
possible during the second or third growing season. 
The SNC composition seems to progress slowly in favor 
of grasses on good sites and alfalfa on poor or sandy sites. 
However, stands dominated by alfalfa (>70% coverage) 
remained dominated by alfalfa. The percentage of grass 
